Formation of interconnect structures by removing sacrificial material with supercritical carbon dioxide

ABSTRACT

An inter-layer dielectric structure and method of making such structure are disclosed. A composite dielectric layer comprising a porous matrix, as well as a porogen in certain variations, is formed adjacent a sacrificial dielectric layer. Subsequent to other processing treatments, a portion of the sacrificial dielectric layer is decomposed and removed through a portion of the porous matrix using supercritical carbon dioxide leaving voids in positions previously occupied by portions of the sacrificial dielectric layer. The resultant structure has a desirably low k value as a result of the voids and materials comprising the porous matrix and other structures. The composite dielectric layer may be used in concert with other dielectric layers of varying porosity, dimensions, and material properties to provide varied mechanical and electrical performance profiles.

This is a Divisional Application of Ser. No.: 10/301,976 filed Nov. 21,2002 now U.S. Pat. No. 6,924,222.

BACKGROUND OF THE INVENTION

Low dielectric constant materials are used as interlayer dielectrics inmicroelectronic devices, such as semiconductor devices, to reduce the RCdelay and improve device performance. As device sizes continue toshrink, the dielectric constant of the material between metal lines mustalso decrease to maintain the improvement. Certain low-k materials havebeen proposed, including various carbon-containing materials such asorganic polymers and carbon-doped oxides. Although such materials mayserve to lower the dielectric constant, they may offer inferiormechanical properties such as poor strength and low fracture toughness.The eventual limit for a dielectric constant is k=1, which is the valuefor a vacuum. Methods and structures have been proposed to incorporatevoid spaces or “air gaps” using, for example, sacrificial materials, inattempts to obtain dielectric constants closer to k=1. One major issuefacing such technologies is how to remove sacrificial material fromrelatively small or relatively large volumes to facilitate multi-layerstructures with voids. Another major issue facing such technology is howto facilitate void creation while providing a structure which canwithstand modern processing treatments, such as chemical-mechanicalpolishing and thermal treatment, as well as post processing mechanicaland thermo-mechanical rigors.

Accordingly, there is a need for a microelectronic structureincorporating voids which has low-k dielectric properties, can be usedin multi-layer structures, and has acceptable mechanical characteristicsduring and after processing.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and is notlimited in the figures of the accompanying drawings, in which likereferences indicate similar elements. Features shown in the drawings arenot intended to be drawn to scale, nor are they intended to be shown inprecise positional relationship.

FIGS. 1A-1B depict cross-sectional views of various aspects of oneembodiment of the present invention incorporating a sacrificialdielectric layer soluble in supercritical carbon dioxide.

FIGS. 2A-2J depict cross-sectional views of various aspects of a relatedembodiment of the present invention incorporating a sacrificialdielectric layer soluble in supercritical carbon dioxide.

FIGS. 3A-3B depict cross-sectional views of various aspects of anotherembodiment of the present invention incorporating an additionaldielectric layer between the sacrificial dielectric layer and thesubstrate.

DETAILED DESCRIPTION

In the following detailed description of embodiments of the invention,reference is made to the accompanying drawings in which like referencesindicate similar elements. The illustrative embodiments described hereinare disclosed in sufficient detail to enable those skilled in the art topractice the invention. The following detailed description is thereforenot to be taken in a limiting sense, and the scope of the invention isdefined only by the appended claims.

This invention involves the use of supercritical carbon dioxide (alsodenominated “supercritical CO₂” or “scCO₂”) to remove at least a portionof the material comprising the sacrificial dielectric layer, subsequentto other process treatments such as electroplating or planarizationwhich may be facilitated by the presence of intact dielectric layers.The sacrificial layer may be positioned adjacent another dielectriclayer which is also modified upon exposure to supercritical CO₂. Anexample scenario is depicted in brief in FIGS. 1A and 1B.

Referring to FIG. 1A, a substrate layer (200) is depicted adjacent asacrificial dielectric layer (202). The sacrificial dielectric layer(202) is positioned between the substrate layer (200) and a seconddielectric layer (210), and is at least partially crossed by twoconductive layers (218, 220), one of which (220) is shown completelycrossing the sacrificial dielectric layer (202) to form an electricalconnection across the sacrificial dielectric layer, as is commonly seenin microelectronic interconnects. The dielectric materials comprisingthe sacrificial dielectric layer (202) and the second dielectric layer(210) provide structural support which assists in maintaining theposition of the conductive layers (218, 220), and provide loaddistribution and resistance as forces are applied to adjacent layers,such as during planarization. While such support is desirable formechanical reasons, it can be related to decreased dielectricperformance, as compared with dielectric layers comprising, at least inpart, air gaps or voids. To increase dielectric performance, voids arecreated in the sacrificial layer, and in other embodiments, in thesecond dielectric layer, subsequent to processing treatments which mayrequire or be facilitated by the mechanical support provided bycompletely intact layers.

Referring to FIG. 1B, a version of the structure previously depicted inFIG. 1A is shown, this variation having improved dielectric propertiesprovided by at least one void positioned in the volume (206) previouslyoccupied by the sacrificial dielectric layer, and a modified seconddielectric layer (214) also defining voids, the voids in each of theselayers being created as a result of exposure to supercritical carbondioxide, or supercritical carbon dioxide and co-solvents. Fornomenclature efficiency, in the term “supercritical carbon dioxide” isused in reference to both supercritical carbon dioxide and co-solventsof supercritical carbon dioxide, as would be known to one skilled in theart. Supercritical carbon dioxide, known to penetrate small geometriesand absorb and transport decomposed materials, may also be used toremove porogen decompositions within the second dielectric layer (210).The use of supercritical carbon dioxide requires fairly high pressures,in the range of 1,071 p.s.i. to reach the critical point of carbondioxide, and special process equipment and environments, as isconvention to those skilled in the art. To clarify the simplifiedterminology used herein as associated with the thermal or chemicalbreak-down of sacrificial materials for subsequent removal, referencesto “decompositions” and “decomposing” comprise reference to “dissolving”and “dissolution” as well, or more simply, “break-down” by thermal orchemical means. The novel process and structures associated withconversion between structures such as those of FIGS. 1A and 1B areillustrated in further detail in FIGS. 2A-2J. It is important to notethat while a damascene type process is illustrated in FIGS. 2A-2J,wherein the conductive layer is formed into trenches usingelectroplating techniques, the dielectric aspect of the invention,illustrated in summary fashion with the transformation from structureslike that of FIG. 2C to structures like that of FIG. 2D, may besimilarly applied to structures formed using other conventionaltechniques for forming conductive layers, such as subtractivemetallization, given that the appropriate materials are in place asfurther described below. As would be apparent to one skilled in the art,subtractive metallization may involve formation of adjacent dielectriclayers after formation of conductive layers, and the geometries ofconductive layers formed may vary from those available withelectroplating processes such as dual damascene.

Referring to FIG. 2A, a substrate layer (200) is shown, upon which asacrificial dielectric layer (202) has been formed. The substrate layer(200) may be any surface generated when making an integrated circuit ormicroelectronic device, upon which a conductive layer may be formed. Thesubstrate layer (200) thus may comprise, for example, active and passivedevices that are formed on a silicon wafer, such as transistors,capacitors, resistors, diffused junctions, gate electrodes, localinterconnects, etcetera. The substrate layer (200) may also compriseinsulating materials (e.g., silicon dioxide, either undoped or dopedwith phosphorus or boron and phosphorus; silicon nitride; siliconoxynitride; or a polymer) that separate active and passive devices fromthe conductive layer or layers that are formed adjacent them, and maycomprise other previously formed conductive layers. The sacrificialdielectric layer (202) comprises a dielectric material substantiallysoluble in supercritical carbon dioxide, such as a highly-fluorinated orsiloxane-based polymer dielectric material, many of which are commonlyused in semiconductor processing. Example dielectric materials solublein supercritical carbon dioxide include, but are not limited to,poly(vinylidene fluoride), poly(tetrafluoroethylene),perfluoropolyethers, perfluoro(meth)acrylates, poly(dimethyl siloxane),and highly-branched poly(perfluorooctylacrylate) (“pFOA”). Thesedielectric materials may be applied by various methods, depending on thechemistry of the material: spin-casting out of solution, evaporativedeposition, physical vapor deposition, or chemical vapor deposition. Thesacrificial dielectric layer (202) may be deposited in thicknessespreferably between about 10 nanometers to about 2000 nanometers.Additionally, co-solvents and reagents may be used to increase thesolubility of some dielectric materials in scCO2 and extend the numberof materials that can be used as the sacrificial dielectric material.These co-solvents and reagents include, but are not limited to, aproticsolvents (e.g., acetone, N-methyl pyrrolidinone, dimethyl sulfide, anddimethyl sulfoxide), protic solvents (e.g., water, methanol, or higheralcohols), organic solvents (e.g., hexanes), and reagents which attackthe sacrificial dielectric material (e.g., hydrogen fluoride).

Referring to FIG. 2B, two conductive layers (218, 220) have been addedto the structure of FIG. 2A. Each of the conductive layers (218, 220),comprising materials conventionally used to form conductive layers inintegrated circuits, and preferably comprising metals such as copper,aluminum, and alloys thereof, is formed using known techniques. Forexample, the second depicted conductive layer (220) is formed usingknown dual damascene techniques, wherein a trench is formed usingconventional lithography, etching, and cleaning techniques, the trenchhaving a via portion (223) and a line portion (225), the line portionhaving a width varying from about 10 nanometers to about 2000nanometers. The trench may then be lined with a barrier layer (notshown) to isolate conductive material, after which the trench is filledwith a conductive material using, for example, known electroplating,chemical vapor deposition, or physical deposition techniques, to formthe conductive layer (220) shown. With copper metal conductive layers, abarrier layer comprising, for example, tantalum, tantalum nitride ortungsten, is effective for isolating the copper. Such barrier layers maybe deposited using conventional techniques such as chemical vapordeposition, atomic layer deposition, or other techniques as would beapparent to those skilled in the art, preferably at a thickness betweenabout 10 nanometers and about 50 nanometers. Known polymeric barrierlayers may also be employed, subject to the requirement that they beselected from the subgroup of polymer barrier materials which haverelatively good electromigration characteristics, and be substantiallyinsoluble in supercritical carbon dioxide.

Similarly, the first depicted conductive layer (218) may be formed usingdamascene techniques, this example, however, not having a “via” portionextending toward the substrate layer (200). The resultant interconnectstructure has conductive layers (218, 220) positioned between remainingportions of the sacrificial dielectric layer (202). Alternatively,conductive layers (218, 220) may be made from doped polysilicon or asilicide, e.g., a silicide comprising tungsten, titanium, nickel, orcobalt, using known techniques. Depending upon the selected conductivematerial, a shunt layer may be formed over the conductive layers usingconventional techniques and materials, to isolate the conductive layersfrom subsequent treatments and materials. With copper metal conductivelayers, a metal shunt layer comprising, for example, cobalt or tungsten,is effective for isolating the copper. The shunt material (not shown)may be deposited at a thickness between 5 nanometers and 100 nanometers,preferably between 10 nanometers and 50 nanometers, using conventionaltechniques such as chemical vapor deposition, subsequent to aplanarization using known techniques such as chemical-mechanicalplanarization (hereinafter “CMP”). Shunt material deposited upon theexposed portions of the sacrificial dielectric layer (202) may beremoved using subsequent CMP or etch back treatments, as would beapparent to those skilled in the art.

Referring to FIG. 2C, a structure similar to that of FIG. 2B isdepicted, with the exception that a second dielectric layer (210) hasbeen deposited adjacent the conductive layers (218, 220) and exposedportions of the sacrificial dielectric layer (202). To facilitate theintroduction of supercritical carbon dioxide to the sacrificialdielectric layer (202), the second dielectric layer (210) may comprise amaterial through which supercritical carbon dioxide may transport to thesacrificial dielectric layer (202), such as a porous material havinginterconnected pores, or the second dielectric layer (210) may comprisea material, or materials in a composition formation, which may betransformed to provide such access to the sacrificial dielectric layer(202). The second dielectric layer (210) generally also must haveelectrically insulative properties, since it is positioned near aconductive layer and generally is not a preferred conduction pathway.

The second dielectric layer (210) preferably comprises a porous matrixhaving interconnected pores which provide a pathway sufficient fortransport of decomposed portions of the sacrificial dielectric layer(202). In a related embodiment, the pores comprising such porous matrixmaterial are at least partially occupied by a removable, or sacrificial,porogen, which may be removed to form a transport pathway for decomposedportions of the sacrificial dielectric layer (202), through theinterconnected pores defined by the porous matrix. A distinction is madebetween a “porous” material having pores, and a material having “voids”,voids differing from pores in that voids are substantially unoccupied bysolid material, whereas pores may or may not be so occupied.

Some preferred porous matrix materials, such as those known as zeolites,have naturally occurring interconnected pores. While the term “zeolite”has been used in reference to many highly-ordered mesoporous materials,several zeolites are known as preferred dielectric materials, such asmesoporous silica and aluminosilicate zeolite materials, each of whichhas a thermal decomposition temperature over 500 degrees, Celsius. Inanother embodiment a polymeric material comprising polystyrene, having athermal decomposition temperature of about 375 degrees Celsius,polymethylmethacrylate (“pMMA”), having a thermal decompositiontemperature of about 330 degrees Celsius, aromatic polycarbonate, havinga thermal decomposition temperature over 440 degrees Celsius, aromaticpolyimide, having a thermal decomposition temperature over 440 degreesCelsius, or silsesquioxanes such as methyl silsesquioxane (“MSQ”) orhydrogen silsesquioxane (“HSQ”), each of which has a thermaldecomposition temperature above 500 degrees Celsius, may be formed intoporous matrix. While single-phase polymers by themselves generally dowill not form interconnected pores, several preferred techniques areavailable to do so. In one embodiment, porogen particles having onedimension larger than the desired matrix film thickness may be used toensure transport channeling across a polymer matrix. In anotherembodiment, modifications to the surface chemistry of a porogenmaterial, or the inherent surface chemistry of porogen materials such asfumed silica, may produce an aggregated structure with highinterconnectivity of porogens. In another embodiment, a polymer matrixmay be combined with a sufficient amount of porogen such that theporogen will define pore interconnectivity within a polymer matrix. Itis known, for example, that porogen loading greater than about 30% byweight percentage is likely to result in pore interconnectivity. Poresdefined by the matrix may have sizes varying from about 5 angstroms toabout 100 nanometers in diameter, depending upon the size of the porogenin the case of most non-zeolite combinations. To facilitate theformation of other adjacent layers with substantially uniform surfaces,pores larger than 10 nanometers in diameter may not be desired.

In one embodiment, the sacrificial porogen may be selectively decomposedand removed from the porous matrix of the second dielectric layer on thebasis of differences in thermal decomposition temperatures between theporous matrix material and the sacrificial porogen. For example, apairing of a sacrificial porogen chosen from the group consisting ofbranched poly(p-xylene), linear poly(p-phenylene), linear polybutadiene,and branched polyethylene, which have thermal decomposition temperaturesof about 425-435 degrees C., about 420-430 degrees C., about 400-410degrees C., and about 400-410 degrees C., respectively, and a porousmatrix material having a higher thermal decomposition temperature,suitable candidates comprising cross-linked poly(phenylene),poly(arylether), aromatic polyimides, and aromatic polycarbonates, eachof which has a thermal decomposition temperature above 440 degrees C.,may contribute to selective removal of a thermally decomposedsacrificial porogen, or a “porogen decomposition”, as facilitated, forexample, by introduction of an oxygen or hydrogen rich carrier plasma tocarry away the decomposition, as is known to those skilled in the art asa standard plasma enhanced carrier technique. Removal may also occur asa byproduct of decomposition, as in the scenario wherein gases carryingportions of a porogen decomposition may be exhausted away from thesecond dielectric layer given an available gradient pathway. Othersuitable materials for use as sacrificial porogens, along with theirrespective thermal decomposition temperatures, include but are notlimited to: Poly(ethylene terephthalate) (“PET”)—about 300 degrees C.,Polyamide-6,6 (“Nylon 6/6”)—about 302 degrees C., Syndiotacticpolystyrene (“PS-syn”) —about 320 degrees C., Poly(e-caprolactone)—about325 degrees C., Poly(propylene oxide) (“PPO”)—about 325-375 degrees C.,Polycarbonates—about 325-375 degrees C., Poly(phenylene sulfide)(“PPS”)—about 332 degrees C., Polyamideimide (“PAI”)—about 343 degreesC., Polyphthalamide (“PPA”, “Amodel”)—about 350 degrees C.,Poly(a-methylstyrene) (“PMS”)—about 350-375 degrees C., Poly(ether etherketone) (“PEEK”)—about 399 degrees C., Poly(ether sulfone) (“PES”)—about400 degrees C., Poly(ether ketone) (“PEK”)—about 405 degrees C.Subsequent to thermal decomposition and removal of decomposed porogenmaterial, the preferred result is a porous matrix interconnected porepathway for subsequent supercritical carbon dioxide introduction to thesacrificial dielectric layer. Thermal decomposition may be facilitatedusing conventional equipment, such as a furnace or oven. Depending uponthe materials selected, plasma tools may be appropriate as well, aswould be apparent to one skilled in the art.

In another embodiment, a sacrificial porogen may be selectivelydecomposed and removed from the porous matrix on the basis of chemicalagent selectivity to the sacrificial porogen. In one variation of suchan embodiment, the sacrificial porogen comprises a material such as ahighly-fluorinated or siloxane-based polymer which is soluble insupercritical carbon dioxide, while the porous matrix material issubstantially insoluble in supercritical carbon dioxide, to enabledecomposition and removal of both a portion of the sacrificial porogenand a portion of the sacrificial dielectric layer in the samesupercritical carbon dioxide exposure treatment, without substantialeffect to the porous matrix material, the result of which is depicted inFIG. 2D. Suitable materials include but are not limited topoly(vinylidene fluoride), poly(tetrafluoroethylene),perfluoro(meth)acrylates, and poly(dimethyl siloxane).Perfluoropolyethers, highly-branched p-FOA, or block copolymers such aspFOA-b-MMA may be used as porogens, for example, and paired with an MSQmatrix, through which portions of the porogen and sacrificial dielectriclayer material may be removed using supercritical carbon dioxide. Blockcopolymers have been used extensively in applications such as removableemulsifiers in supercritical carbon dioxide, and detergent ingredientsfor supercritical carbon dioxide based textile dry cleaning.

Referring to FIG. 2D, the volume (206) previously occupied by thesacrificial dielectric layer (202 of FIGS. 2A-2C) is at least partiallyvacant of solids, defining at least one void which provides desirabledielectric properties as a result of the vacancy. The porous matrixmaterial of the second dielectric layer (210 of FIGS. 2A-2C) remainsintact, and the modified second dielectric layer (214) that it comprisesdefines voids, or interconnected pores at least partially vacant ofsolids, from which portions of the sacrificial porogen have beendecomposed and removed. The arrows (226) in FIG. 2D depict possiblepathways for removal of decomposed dielectric materials through vacatedinterconnected pores or voids. The resultant voids defined by themodified second dielectric layer (214) contribute to preferreddielectric properties surrounding the conductive layers (218, 220).

Summarizing the transformation of the depicted embodiment from thatshown in FIG. 2C to that of FIG. 2D, supercritical carbon dioxide may beintroduced to the intact second dielectric layer, where it decomposesand carries away the scCO₂-soluble sacrificial porogen to leave apathway of interconnected pores (226), through which supercriticalcarbon dioxide is introduced to the scCO₂-soluble sacrificial dielectriclayer. The supercritical carbon dioxide then decomposes at least aportion of the sacrificial dielectric layer to form a sacrificialdielectric layer decomposition, which is carried away through theinterconnected pore pathway with the supercritical carbon dioxide,leaving behind at least one void in a position previously occupied bythe material comprising the sacrificial dielectric layer. Thedecomposition and removal of sacrificial porogen and sacrificialdielectric layer material may all occur in one supercritical carbondioxide exposure. In another embodiment, a portion of the porogen may bethermally decomposed and removed from the porous matrix material viadiffusion or as facilitated by a carrier plasma, to create a pathway ofinterconnected voids through which supercritical carbon dioxide may beused to decompose and remove the sacrificial dielectric layer. Inanother embodiment, the second dielectric layer may comprise a porousmatrix without a porogen, such as a zeolite material, in which case apathway of interconnected voids is available to facilitate decompositionand removal of the sacrificial dielelctric material through suchpathway.

Referring back to FIG. 2C, the depicted embodiment of the seconddielectric layer (210) preferably is formed using a variety ofconventional techniques, such as spin coating, chemical vapordeposition, or plasma-enhanced chemical vapor deposition. Depending uponthe pore interconnectivity modality, discussed above, and associatedmaterials, the appropriate thickness of the second dielectric layer(210) will vary. Pairings of the aforementioned preferred porogen andmatrix materials are preferably deposited together using conventionalspin coating or chemical vapor deposition techniques, with a depositionthickness preferably between about 5 nanometers and 100 nanometers.Zeolite materials may be synthesized by an aerogel or xerogel process,spin-coated into place, or deposited using chemical vapor deposition toform a porogen-free porous structure upon deposition. In the case ofspin coating or other deposition methods, solvent may need to be removedusing evaporative techniques familiar to those skilled in the art.

Referring to FIG. 2E, a sealing layer (228) may be deposited adjacentthe transformed second dielectric layer (214) to isolate the transformedsecond dielectric layer (214) from other subsequently formed layers, toprovide a relatively uniform surface onto which other surfaces may bemore homogeneously formed, as compared with the porous matrix comprisingthe transformed second dielectric layer (214), and/or to help retaingases, such as nitrogen or argon and/or other inert gases to preventoxidation or corrosion, which may be injected into or trapped within theadjacent layers (206, 214). Preferred sealing layer (228) materialscomprise conventional spin-on glass and spin-on polymeric dielectricmaterials, and chemical-vapor-deposited films such as silicon nitrideand silicon carbide, the sealing layer (228) being deposited in a layerof thickness between about 5 nanometers and about 100 nanometers,preferably between about 10 nanometers and about 50 nanometers.

FIGS. 2F-2H illustrate an embodiment which continues from the structuredepicted in FIG. 2C. FIGS. 2F-2H depict an embodiment of the inventionwherein additional sacrificial layers are added to the structure beforedecomposition and/or transformation of the layers using supercriticalcarbon dioxide. In other words, FIGS. 2F-2H depict an embodiment whereinsupercritical carbon dioxide is introduced to a structure havingmultiple intact sacrificial layers to handle all of the transformationin a single scCO₂ introduction, as opposed to supercritical carbondioxide transformation of each layer separately and sequentially aftereach layer or set of layers (202, 218, 220, and 210 in FIG. 2C, forexample) is completed, as described and illustrated in reference toFIGS. 2D and 2E. Referring to FIG. 2F, a structure similar to that ofFIG. 2C is shown, with the exception that another sacrificial dielectriclayer (204) has been deposited adjacent the intact second dielectriclayer (210). Similarly, FIGS. 2G and 2H parallel FIGS. 2B and 2C, inthat additional conductive layers (222, 224) are formed, for descriptiveconvenience, using similar processes and materials, adjacent to whichanother dielectric layer (212) similar to the second dielectric layer(210) of FIG. 2C is formed. The additional layers added with theprocesses illustrated in FIGS. 2F-2H need not parallel those of FIGS.2A-2C in terms of materials, dimensions, or formation techniques, andmany permutations and combinations of the disclosed aspects of thestructures and methods, as well as variations thereof, are within theintended scope of the invention. Referring to FIG. 2H, the depictedstructure has two intact sacrificial layers (202, 204) and two otherdielectric layers (210, 212) comprising sacrificial porogens positionedwithin the interconnected pores of porous matrix materials making up thetwo dielectric layers (210, 212), the sacrificial layers and sacrificialporogens all being soluble in supercritical carbon dioxide.

FIG. 2I depicts the result of supercritical carbon dioxide exposure tothe structure depicted in FIG. 2H. Porogen decompositions andsacrificial dielectric layer decompositions have exited the structurealong pathways through the interconnected pores of the remaining porousmatrix, such as the pathways illustrated by the arrows (226) in FIG. 2G,to leave behind two layers (206, 208), each of which substantiallycomprises at least one void, and two other layers (214, 216), each ofwhich comprises a porous matrix having interconnected pores, at leastsome of which remain vacated of solid material. Given thehighly-penetrating nature of supercritical carbon dioxide, associatedwith its very low viscosity and surface tension, in addition toappropriately selected sacrificial materials to comprise the sacrificialdielectric layers (202, 204) and the sacrificial porogen which maycomprise the other dielectric layers (214, 216), more than about 80 % ofsuch sacrificial materials may be removed, resulting in relatively largevolumes unoccupied by solids in the positions previously occupied bysuch sacrificial materials. Referring to FIG. 2J, a sealing layer (228)similar to that depicted in FIG. 2E is formed adjacent the transformeddielectric layer (216).

Referring to FIGS. 3A and 3B, another embodiment of the presentinvention is depicted, this embodiment being similar to that of FIGS. 2Cand 2D, with the exception that it has a third dielectric layer (330)formed between the sacrificial dielectric layer (302) and the substratelayer (200). The third dielectric layer (330) may comprise any materialthat may insulate one conductive layer from another. It preferablycomprises a dielectric material not substantially soluble insupercritical carbon dioxide and is positioned to support the conductivelayers (218, 220) and other surrounding structures subsequent tointroduction of supercritical carbon dioxide and concomitant removal ofa portion of the sacrificial dielectric layer (302) to form at least onevoid in its previous position (206), and transformation of the seconddielectric layer (210) to a layer (210) having at least someinterconnected pores which are vacant of solids. In the case of aporogen material for the second dielectric layer (210) which isthermally decomposed, the material comprising the third dielectric layer(330) preferably has a higher thermal decomposition temperature ascompared with the porogen material. As shown in FIG. 3A, theillustrative embodiment of the third dielectric layer (330) is locatedadjacent the via portion (221) of the conductive layer, while the lineportion (223) is adjacent the sacrificial dielectric layer (302). Such aconfiguration adds sustained mechanical integrity to the relativelynarrow via portion, and also provides desirable insulative propertiesmost closely adjacent the line portion (223) of the conductive layer. Anadditional non-scCO2 soluble dielectric layer such as that depicted inFIGS. 3A and 3B maybe added to structures such as those depicted inFIGS. 2F-2J for added structural integrity.

The third dielectric layer (330) may comprise silicon dioxide (eitherundoped or doped with phosphorus or boron and phosphorus); siliconnitride; silicon oxy-nitride; porous oxide; an organic containingsilicon oxide; or a polymer. Silicon dioxide, silicon nitride, andsilicon oxy-nitride preferably have relatively high mechanical strengthcharacteristics as compared with many suitable porous matrix materials.Also preferred are polymers or carbon doped oxides, as further describedbelow, with a low dielectric constant: preferably less than about 3.5and more preferably between about 1.5 and about 3.0. The thirddielectric layer (330) may also comprise may comprise an organic polymerselected from the group consisting of polyimides, parylene,polyarylethers, organosilicates, polynaphthalenes, and polyquinolines,copolymers thereof, or other polymers not soluble in supercriticalcarbon dioxide. For example, commercially available polymers sold byHoneywell Corporation and Dow Chemical Corporation under the trade namesFLARE™ and SiLK™, respectively, may be used to form the third dielectriclayer (330).

The third dielectric layer (330) may alternatively comprise a compoundhaving the molecular structure Si_(x)O_(y)R_(z), in which R is selectedfrom the group consisting of hydrogen, carbon, an aliphatic hydrocarbonand an aromatic hydrocarbon. When “R” is an alkyl or aryl group, theresulting composition is often referred to as carbon-doped oxide(“CDO”). When the third dielectric layer (330) comprises a carbon-dopedoxide, it preferably comprises between about 5 and about 50 atom %carbon. More preferably, such a compound includes about 15 atom %carbon.

Examples of other types of materials that may be used to form the thirddielectric layer (330) include zeolites, aerogel, xerogel, andspin-on-glass (“SOG”). In addition, the third dielectric layer (330) maycomprise either hydrogen silsesquioxane (“HSQ”), methyl silsesquioxane(“MSQ”), or other materials having the molecular structure specifiedabove, which may be coated onto the surface of a semiconductor waferusing a conventional spin coating process. Although spin coating may bea preferred way to form the third dielectric layer (330) for somematerials, for others chemical vapor deposition, plasma enhancedchemical vapor deposition, a SolGel process, or foaming techniques maybe preferred.

The third dielectric layer (330) may also comprise a porous matrix, or aporous matrix and removable porogen combination, analogous to thosedescribed above in reference to the dielectric layers (210, 212) ofFIGS. 1 and 2. Should a porogen material of a second dielectric layer, asacrificial dielectric material, and a porogen material of a thirddielectric layer all be soluble in supercritical carbon dioxide, asingle supercritical carbon dioxide exposure may be used fordecomposition and removal thereof. When the third dielectric layer (330)comprises a polymer, it is preferably formed by spin coating or chemicalvapor depositing the polymer onto the surface of substrate (200), usingconventional equipment and process treatments. The third dielectriclayer (330) may have a thickness between about 10 nanometers and about1000 nanometers, preferably between about 20 nanometers and about 500nanometers. The sacrificial dielectric layer (302) depicted in FIGS. 3Aand 3B may be a material similar to the materials described above inreference to FIGS. 2, the key difference between the sacrificialdielectric layer (302) of the illustrative example of FIGS. 3 and thesacrificial dielectric layer of the illustrative example of FIGS. 2(202) being the addition of the third dielectric layer (330) adjacentthe sacrificial dielectric layer (302) of FIGS. 3.

Thus, a novel dielectric solution is disclosed. Although the inventionis described herein with reference to specific embodiments, manymodifications therein will readily occur to those of ordinary skill inthe art. Accordingly, all such variations and modifications are includedwithin the intended scope of the invention as defined by the followingclaims.

1. A microelectronic structure comprising: a substrate layer; asacrificial dielectric layer; a second dielectric layer comprising aporous matrix material defining interconnected pores, the sacrificialdielectric layer being positioned between the substrate layer and thesecond dielectric layer; and at least two conductive layers, each ofwhich extends substantially perpendicularly at least partially across aregion of the sacrificial dielectric layer between the substrate layerand second dielectric layers, and each of which extends laterally, andsubstantially parallel to the substrate layer, over a region of thesacrificial dielectric layer; wherein the sacrificial dielectric layerdefines one or more voids occupying more than about 80% of the volumeoccupied by the sacrificial dielectric layer.
 2. The microelectronicstructure of claim 1 wherein the porous matrix material is substantiallyinsoluble in supercritical carbon dioxide.
 3. The microelectronicstructure of claim 1 wherein the second dielectric layer furthercomprises a porogen material residing within more than one of theinterconnect pores.
 4. The microelectronic structure of claim 3 whereinthe porogen material is soluble in supercritical carbon dioxide.
 5. Themicroelectronic structure of claim 3 wherein the porogen material has alower thermal decomposition temperature than the porous matrix material.6. The microelectronic structure of claim 3 wherein at least onediffusion pathway is formed across the second dielectric layer byinterconnected pores which are not occupied by a solid.
 7. Themicroelectronic structure of claim 3 wherein less than 80% of theinterconnected pores are occupied by a solid.
 8. The microelectronicstructure of claim 1 further comprising a third dielectric layerpositioned between the sacrificial dielectric layer and the substratelayer, the third dielectric layer comprising a material substantiallyinsoluble in supercritical carbon dioxide.
 9. The microelectronicstructure of claim 1 further comprising a sealing layer positionedopposite and adjacent the second dielectric layer from the sacrificialdielectric layer, the sealing layer isolating the second dielectriclayer from other layers and providing a relatively uniform surface ontowhich other layers may be formed.
 10. The microelectronic structure ofclaim 1 wherein the sacrificial dielectric layer is soluble insupercritical carbon dioxide.
 11. The microelectronic structure of claim1 wherein the sacrificial dielectric layer comprises ahighly-fluorinated or siloxane-based polymer.
 12. The microelectronicstructure of claim 11 wherein the sacrificial dielectric layer comprisesa polymer from the list consisting of poly(vinylidene fluoride),poly(tetrafluoroethylene), perfluoropolyether, perfluoro(meth)acrylate,poly(dimethyl siloxane), and pFOA.
 13. The microelectronic structure ofclaim 1 wherein the porous matrix material of the second dielectriclayer comprises a polymer-based material from the list consisting ofpolystyrene, polymethylmethacrylate, aromatic polycarbonate, aromaticpolyimide, methyl silsesquioxane, hydrogen silsesquioxane, cross-linkedpoly(phenylene), and poly(arylether).
 14. The microelectronic structureof claim 1 wherein the porous matrix material comprises a zeolite. 15.The microelectronic structure of claim 4 wherein the porogen materialcomprises a supercritical carbon dioxide soluble material from the listconsisting of a highly-fluorinated polymer, a siloxane-based polymer,and a block copolymer.
 16. The microelectronic structure of claim 5,wherein the porogen material comprises a material from the listconsisting of branched poly(p-xylene), linear poly(p-phenylene), linearpolybutadiene, branched polyethylene, PET, Nylon 6/6, PS-syn,poly(e-caprolactone), PPO polycarbonate, PPS, PAI, PPA, PMS, PEEK, andPEK.
 17. A microelectronic structure comprising: a substrate layer; aporous dielectric layer; a sacrificial dielectric layer positionedbetween the substrate layer and the porous dielectric layer, thesacrificial layer defining one or more voids occupying more than about80% of the volume occupied by the sacrificial dielectric layer; and atleast two conductive layers, wherein each of which extends substantiallyperpendicularly at least partially across a region of the sacrificialdielectric layer between the substrate layer and second dielectriclayer, and wherein each of which extends laterally, and substantiallyparallel to the substrate layer, over a region of a void in thesacrificial layer.
 18. The microelectronic structure of claim 17 whereinthe porous dielectric layer is substantially insoluble in supercriticalcarbon dioxide.
 19. The microelectronic structure of claim 17 whereinthe porous dielectric layer further comprises a porogen materialresiding within more than one pores.
 20. The microelectronic structureof claim 19 wherein the porogen material is soluble in supercriticalcarbon dioxide.
 21. The microelectronic structure of claim 20 whereinthe sacrificial dielectric layer is soluble in supercritical carbondioxide.
 22. A microelectronic structure comprising: a substrate layer;a porous dielectric layer; a sacrificial dielectric layer positionedbetween the substrate layer and the porous dielectric layer, thesacrificial layer including a sacrificial material and one or more voidsoccupying more than about 80% of the volume occupied by the sacrificiallayer; and at least two conductive layers, wherein each of which extendssubstantially perpendicularly at least partially across a region of thesacrificial dielectric layer between the substrate layer and seconddielectric layer, and each of which is at least partially positionedabove an adjacent single void of the sacrificial layer.
 23. Themicroelectronic structure of claim 17 wherein the porous dielectriclayer is substantially insoluble in supercritical carbon dioxide. 24.The microelectronic structure of claim 17 wherein the porous dielectriclayer further comprises a porogen material residing within more than onepores.
 25. The microelectronic structure of claim 19 wherein the porogenmaterial and sacrificial dielectric layer are soluble in supercriticalcarbon dioxide.